The cleaning was targeted around the patient bed
The NHS is being urged to invest more in cleaners after research showed just one extra worker can make a difference.
The Unison-sponsored study showed having one more cleaner on a ward could reduce bugs by a third, potentially saving lives and money.
But despite the evidence, the union said it was concerned about the future of hospital cleaning services.
The government said cleaning was already a priority - as its record in reducing superbug rates showed.
The Unison study was carried out at Glasgow's Southern General Hospital by leading infections expert Dr Stephanie Dancer.
She analysed the impact of employing an extra cleaner on a ward for six months and then repeated it on another ward for the same length of time.
She found contamination of surfaces was reduced by 32.5% overall. Just four MRSA infections were confirmed in patients during the extra cleaning period, compared to nine during the period when there was no extra worker.
The cleaner was asked to focus on specific areas close to the patient beds, including lockers, trays, curtains and rails.
Dr Dancer said: "We should not forget that basic hospital cleaning with detergent and water is the first line of defence against hospital infections."
The research was published in the BMC Medicine journal to coincide with a one-day conference held in London on Tuesday by Unison for hospital cleaners.
The union is concerned about the future of hospital cleaning with the move towards contracting out services - 40% of hospitals use private cleaning firms - and the financial pressures being felt across the public sector because of the recession.
Control of infections
Unison general secretary Dave Prentis said: "Armed with this evidence, Unison will be arguing that every cleaner plays an invaluable part in the control of infections."
But the government said it had made cleaning a priority in recent years in its fight against superbugs.
In England, MRSA rates are now a quarter of their peak of 2004. Falls have also been seen in the rest of the UK.
A Department of Health spokeswoman said: "The hard work of NHS staff, together with our strategy for reducing infection, are continuing to deliver real improvements in clean, safe care for patients."
And she added: "Preventing infections continues to be a top priority for the government and we welcome this contribution that demonstrates the importance of infection control and cleaning teams working closely together."